Systems and methods for interrogator multiple radio frequency identification enabled documents

ABSTRACT

A multi-document read-write station provides the ability to read/write to a stack of Radio Frequency Identification (RFID) tags within a small area. Specifically, the station provides the ability to read from and write to a tall stack of RFID tagged sheets with the RFID tags stacked one on top of the other. The station and capability described herein is the result of and comprises several components including a closed chamber comprising a document slot, an antenna system, and a power management system.

RELATED APPLICATIONS INFORMATION

This application claims priority under 35 U.S.C. 119(e) to ProvisionalPatent Application Ser. No. 60/805,423, entitled “An RFID Smart Cabinetand a Multi-Document Read Write Station,” filed Jun. 21, 2006, which isincorporated herein by reference as if set forth in full.

BACKGROUND

1. Field

The field of the invention relates generally to Radio FrequencyIdentification (RFID) systems and more particularly to systems andmethods for reading and writing information from multiple RFID enableddocuments.

2. Background

FIG. 1 illustrates a basic RFID system 100. A basic RFID system 100comprises three main components: an antenna or coil 104; an interrogator102, and a transponder, or RF tag 106 which is often electronicallyprogrammed with unique information. Antenna 104 can be configured toemit radio signals 108 to activate tag 106 and read and write data fromthe activated tag 106. Antenna 104 is the conduit between tag 106 andinterrogator 102, which is typically configured to control dataacquisition and communication. Antennas 104 are available in a varietyof shapes and size. For example, in certain embodiments they can bebuilt into a door frame to receive tag data from persons or thingspassing through the door. In other embodiments, antennas 104 can, forexample, be mounted on an interstate toll booth to monitor trafficpassing by on a freeway. Further, depending on the embodiments, theelectromagnetic field, i.e., radio signal 108, produced by an antenna104 can be constantly present when, e.g., multiple tags 106 are expectedcontinually. If constant interrogation is not required, then radiosignal 108 can, for example, be activated by a sensor device.

Often antenna 104 is packaged with interrogator 102. A conventionalinterrogator 102 can emit radio signals 108 in ranges of anywhere from 1inch to 100 feet or more, depending upon the power output and the radiofrequency used. When an RFID tag 106 passes through an electromagneticzone associated with radio signal 108, it detects radio signal 108,which can comprise an activation signal. In some embodiments,interrogators can comprise multiple antenna, though typically only onetransmits at a time.

Additionally, interrogator 102 is often coupled through network 110 to acentral server 112. Central server 112 can be configured to execute anumber of applications including those that incorporate data from RFIDtags 106. For example, in a tracking system, interrogator 102 transmitsto the central server 112 the identity of tags that have passed throughits interrogation zone. This information can be correlated to objectsassociated with the tag in a database residing on the central server andhence the whereabouts of the object in question at that particular timecan be logged. In the example of a toll booth, tags that pass throughthe specific toll both are reported to central server 112, whichcorrelates the tag to a motorist who is then debited the cost of thetoll.

RFID tags 106 come in a wide variety of shapes and sizes. Animaltracking tags inserted beneath the skin, for example, can be as small asa pencil lead in diameter and one-half inch in length. Tags 106 can bescrew-shaped to be inserted into trees or wooden items foridentification purposes, or credit-card shaped for use in accessapplications. Anti-theft hard plastic tags attached to merchandise instores can include RFID tags. In addition, heavy-duty RFID tags can beused to track containers, heavy machinery, trucks, and/or railroad carsfor maintenance and/or tracking purposes.

RFID tags 106 are categorized as either active or passive. Active RFIDtags 106 are powered by an internal battery and are typicallyread-write, i.e., tag data can be rewritten and/or modified. An activetag's memory size varies according to application requirements. Forexample, some systems operate with up to 1 MB of memory. Thebattery-supplied power of an active tag 106 generally gives it a longerread range. The trade off is greater size, greater cost, and a limitedoperational life.

Passive RFID tags 106 operate without a separate external power sourceand obtain operating power from radio signal 108. Passive tags 106 areconsequently much lighter than active tags 106, less expensive, andoffer a virtually unlimited operational lifetime. The trade off is thatthey have shorter read ranges than active tags 106 and require ahigher-powered interrogator 102. Read-only tags 106 are typicallypassive and are programmed with a unique set of data, usually 32 to 128bits, that cannot be modified. Read-only tags 106 often operate in thesame way as linear barcodes. It should be noted that passive tags canalso be used in read-write systems.

RFID systems are also distinguishable by their frequency ranges.Low-frequency, e.g., 30 KHz to 500 KHz, systems 100 have short readingranges and lower system costs. They are commonly used in securityaccess, asset tracking, and animal identification applications.High-frequency, e.g., 850 MHz to 950 MHz and 2.4 GHz to 2.5 GHz 100systems offer long read ranges, e.g., greater than 90 feet, high readingspeeds, and are used for such applications as railroad car tracking andautomated toll collection; however, the higher frequency RFID systems100 typically result in higher system costs.

RFID systems employ a type of modulation known as backscattermodulation. In a backscatter system, the tags do not generate their ownRF carrier signal. Rather, interrogator 102 generates a carrier signalthat it broadcasts within its coverage area. The tags then reflect thissignal back to interrogator 102. The reflection of the carrier signal istermed backscatter. In order to communicate information on thebackscattered signal, the tag will alternatively reflect and not reflectthe signal in order to indicate “1”s and “0”s to interrogator 102. Thisis termed backscatter modulation.

The significant advantage of all types of RFID systems 100 is thenoncontact, non-line-of-sight nature of the technology. Tags 106 can beread through a variety of substances such as snow, fog, ice, paint,crusted grime, and other visually and environmentally challengingconditions, where barcodes or other optically read technologies cannottypically be used. RFID tags 106 can also be read in challengingcircumstances at high speeds, often responding in less than 100milliseconds. RFID has become indispensable for a wide range ofautomated data collection and identification applications that would notbe possible otherwise.

One area where passive RFID tags have proven potentially useful is intracking documents. For example, a passive RFID tag shaped like a smallsticker, or label can be affixed to a highly confidential document inorder to track access to and the location of the document. In otherwords, if someone wants to access the document, which can be stored in acabinet, then they can be required to scan the document out. Likewise,they can be required to scan the document in once they have returned it.In this manner, a record of when the document is “checked-out” can bemaintained. Such a process can be combined with security mechanismlimiting access to the cabinet as well as a mechanism to log who checkedthe document out.

Such a system, however, can prove cumbersome if there a many documentsbeing checked in an out by multiple users. For example, in aconventional system, each document must be scanned in and outindividually, otherwise the tags on each document will interfere witheach other. RFID tags suffer from detuning and cross coupling (sharingenergy) when two or more tags are placed in each other's effective area.The effective area is ¼ of the Radio Frequency (RF) wave length. Forexample, at 2401 MHz this is equivalent to 1.2 inches. When a documentis tagged and then stacked on top of another tagged document, the resultare two tag documents where the RFID tag is separated only by thethickness of the sheet of paper. This separation is insufficient toallow the two tags to work optimally resulting in the inability of theinterrogator to communicate properly to the RFID tag. This problem iscompounded when more tag documents are stacked.

SUMMARY

A multi-document read-write station provides the ability to read/writeto a stack of Radio Frequency Identification (RFID) tags within a smallarea. Specifically, the station provides the ability to read from andwrite to a tall stack of RFID tagged sheets, or documents with the RFIDtags stacked one on top of the other. The station and capabilitydescribed herein is the result of and comprises several componentsincluding a closed chamber comprising a document slot, an antennasystem, and a power management system.

In one aspect, the chamber walls can be conductive to maintain highfield strength around the documents and generate a specific mode withrespect to the Radio Frequency (RF) signals. The chamber wall can, forexample, be metalized using a metallic film or perforated metal tocontain the RF energy and allow light through simultaneously so that thechamber contents are visible.

In another aspect, the chamber can comprise a non conductive documentslot that holds the RFID tagged documents and positions them in thechamber where the field strength is high. The chamber can have an accessdoor with an interlock to prevent radiation while being loaded orunloaded.

In another aspect, the slot can be constructed at an angle to force thedocuments to slide to the end of the slot. Additionally, the end of thedocument slot can be angled to introduce tag offset separation andgreater tag spacing.

In another aspect, the chamber's dimensions can be configured toresonate at a given frequency for a given number of modes.

In another aspect, multiple radiating elements (antennas) can beincluded to facilitate the reading/writing of items.

In another aspect, one power setting can be used for reading and anelevated power setting for writing. Since passive RFID needs more powerto write then to read, having separate power setting for the read andwrite process can reduce the tags exposure to high power.

In another aspect, the RFID tags can be tuned specifically for thisenvironment by introducing thin features to reduce detuning effects andgreater efficiency when placed inside a stack of documents.

These and other features, aspects, and embodiments of the invention aredescribed below in the section entitled “Detailed Description.”

BRIEF DESCRIPTION OF THE DRAWINGS

Features, aspects, and embodiments of the inventions are described inconjunction with the attached drawings, in which:

FIG. 1 is a diagram illustrating a conventional RFID system;

FIG. 2 is illustrates a document that includes an RFID tag for use inconjunction with the systems and methods described herein; and

FIG. 3 is a diagram illustrating an example multi-document read-writestation configured in accordance with one embodiment.

DETAILED DESCRIPTION

The embodiments described below are directed to systems and methods forreading from and writing to multiple RFID tags on multiple documents,especially when the documents are stacked on top of each other. Itshould be pointed out, however, that the embodiments described hereinare by way of example only and should not be seen as limiting thesystems and methods described herein to particular configurations,processes, or applications. For example, the systems and methodsdescribed herein can be used with other tagged items.

FIG. 2 illustrates a document 200 that comprises an RFID tag 202. RFIDtag 202 can comprise a chip that includes the circuitry necessary topower the tag and perform required functions, as well as memory to storeinformation. RFID tag 202 can be a read only tag or a read-write tagdepending on the embodiment. Identifying information, i.e., informationidentifying document 200 can be written into the memory of tag 202either in the factory or after tag 202 is affixed to document 200.

The chip can be coupled with an antenna configured to resonant at acertain frequency, or frequencies. The antenna can be formed fromconductive material such as metal. Alternatively, and often preferable,the antenna can be formed from a conductive paste or ink applied to athin substrate such as a plastic substrate. Thus, the antenna can beformed on the substrate and the chip can then be coupled to the antenna,e.g., using a conductive adhesive. An adhesive layer can then be appliedto the back of the substrate so that it can be applied like a sticker,or label to document 200.

FIG. 3 is a diagram illustrating a multi-document read-write station 300configured in accordance with one embodiment. Station 300 comprises achamber 301 with a slot 302 into which documents 304, e.g., documentssuch as document 200, can be placed wither when being checked out orchecked in. It will be understood that FIG. 3 provide a cross sectionalview of station 300 and that chamber walls 308 will actually surroundslot 302. Chamber walls 308 can be conductive to maintain high fieldstrength around slot 302 and to generate a specific mode, or modes ofoperation with respect to the RF signals being generated. For example,walls 308 can be made conductive via a metalized film applied to thechamber walls. Alternatively, chamber walls 308 can be made from metal.

For example, in one embodiment, at least some of walls 308 can beconstructed from perforated metal to contain the RF energy and allowlight through simultaneously so that the chamber contents, i.e.,documents 304, are visible.

Slot 302 can be non-conductive, i.e., be formed from no-conductive walls306. Slot 302 can be configured to hold RFID tagged documents 304 andposition them within chamber 301 where the RF field strength is high.The RF field is generate by one or more antennas 310 position near, oraround slot 302. It will be understood that antennas 310 are interfacedwith and interrogator (not shown), such as interrogator 102 describeabove.

Slot 302 can be constructed at an angle (α) to force documents 304 toslide to the end of the slot. Additionally, slot 302 comprises an angledstop wall 314 to introduce tag offset separation and greater tagspacing. In other words, by including stop wall 314 angled at angle (β),the tops of documents 304 will be offset with respect to each other.Assuming that the RFID tags, e.g., tags 202, are placed at the samelocation on each document, then this will also create and offset in thelocation of each tag with respect to the other tags. This reduces thedetuning and cross coupling referred to above and enables reading oftags from multiple documents.

It will be understood that the dimensions of slot 302, the location ofthe tags on the documents, and the angels (α) and (β), will all dependon the requirements of specific implementation, including the documentssize, frequency being used, dimensions of chamber 301, etc. In thisregard, the dimensions of chamber 301 can be configured so that chamber301 will resonate at a given frequency and for a given number of modes.As a result, the RF field can be effectively amplified allowing lowerpower system design and increasing write capabilities.

In a large stack of documents 304, the greatest amount of cross couplingwill occur in the middle of the stack. As a result, tags in the middleof the stack will require greater read and write energies. Conversely,tags located on the top and bottom will require less energy than tags inthe middle. Since the system must be designed to read and write to tagsin the middle, the resulting energy levels can be too high for properoperation of tags on the top and bottom.

The RF energy, e.g. produced by antennas 310 is converted by the tagchip into a voltage that can be used to power the tag. If the energy istoo high, then this can result a chip voltage that is too high forproper operation of the tags on top and bottom. To correct for this,attenuation and or detuning pads (not shown) can be placed on the topand bottom of slot 302 to attenuate and or detune the top and bottomtags so that the chip voltage is the same level as that of the tags inthe middle.

Certain embodiments can employ harmonic reception of signals beingreturned by the tags. Due to the nature of passive RFID, reception of abackscatter modulation on the carrier signal, or frequency can bechallenging. Allowing the receiver to listen on one or multipleharmonics of the tag aids the system reception. The term harmonic iswell understood and will not be explained here for the sake of brevity.

As illustrated in FIG. 3, multiple radiating elements 310 a, 310 b, and310 c can be used to facilitate the reading/writing of items. It will beunderstood that the use of multiple antennas creates spatial diversity,and possibly phase diversity, which increases the likelihood ofsuccessful reception of the signals. The system can also be configuredto alter the frequency being used to further enhance spatial diversityon any of the active antennas. This requires that antennas 310 as wellas the tag antennas be configured for multi-frequency operation.

To further improve system performance, the antenna system can compriseseparate transmit (310) and receive (312) antennas. Receive antenna 312can be positioned in close proximity to the tags for high sensitivity totags response and at a greater distance to the transmit antennas 310 forhigh isolation, i.e., receive antenna 312 can be positioned at a lowfield strength area. This should result in improved signal to noiseratio when compared to combine transmit and receive systems.

In certain embodiments, for example receive antenna 312 can be an openedended wave guide with directionality. For simplicity, only one receiveantenna 312 can be used; however, in other embodiments multiple receiveantennas 312 can be used.

In certain embodiments, one power setting can be used for reading and anelevated power setting can be used for writing. Since passive RFID needsmore power to write then to read, having separate power setting for theread and write process can reduce exposure to high power RF fields forthe tags.

For example, in one embodiment the system can be configured to rely ontag encode information to determine what power setting to use. This canbe accomplished, for example, by writing information into each tagindicting the number of documents present in slot 302. For example, whenthe first document is placed in slot 302 the number 1 can be writteninto the corresponding tag. When a second document is placed into slot302, then the number 2 can written into each tag. The system can the beconfigured to read this number out of the tags in order to determine apower setting. For example, if the number 10 is read out of documents304, then the system knows that 10 documents are present and it can beconfigured to automatically set the power to the appropriate level for10 documents. By doing this, the system can eliminate the possibly ofoverpowering tags in situation where only 1 exist and under poweringwhen 10 or more exists.

In another embodiment, the transmission power of the interrogator(including antenna) can operate within a range. For example, thetransmission power can start with the minimum power setting with a longtransmission period and a short idle period. The transmission power canthen be cycled upwards at defined intervals. When the transmission powergoes up, the transmission period gets shorter while the idle period getslonger so that the average transmission power is at the same level. Oncethe transmission power reaches the maximum, it should go back to theminimum.

On the tag side, the tags can be tuned specifically for the environmentby introducing thin features to reduce detuning effects and greaterefficiency when placed inside a stack of documents.

Thus, by implementing some or all of the aspects described above amulti-document read-write system capable of reading from and writing tomultiple RFID tagged documents can be constructed. This can greatlyreduce the burden of implementing RFID controlled document systems.

While certain embodiments have been described above, it will beunderstood that the embodiments described are by way of example only.Accordingly, the embodiments should not be limited based on thedescribed embodiments. Rather, embodiments described herein should onlybe limited in light of the claims that follow when taken in conjunctionwith the above description and accompanying drawings.

1. A system for communicating with a plurality of Radio FrequencyIdentification (RFID) tags affixed to a plurality of documents,comprising: a Radio Frequency (RF) radiating antenna for communicatingvia RF signals with the plurality of RFID tags; a chamber comprisingconductive walls, the chamber configured to maintain a high RF fieldstrength; and a slot within the chamber, the slot comprisingno-conductive walls and an angled stop wall, the slot configured to holdthe plurality of documents in a location such that the plurality of RFIDtags are exposed to the high RF field strength and to create an offsetbetween the RFID tags.
 2. The system of claim 1, wherein the chamber isconfigured to resonate at an operational frequency for the system. 3.The system of claim 1, wherein the radiating antenna is configured toreceive RF signals from the plurality of RFID tags, and wherein theradiating antenna is configured to receive harmonic signals from theplurality of RFID tags.
 4. The system of claim 1, further comprising areceive antenna configured to receive RF signals from the plurality ofRFID tags, wherein the receive antenna is separate from the radiatingantenna and positioned close to the plurality of RFID tags.
 5. Thesystem of claim 1, wherein the receive antenna is configured to receiveharmonic signals from the plurality of RFID tags.
 6. The system of claim1, further comprising a plurality of radiating antennas located atdifferent locations within the chamber and around the slot.
 7. Thesystem of claim 1, configured to use multiple frequencies forcommunication with the plurality of RFID tags.
 8. The system of claim 1,wherein a transmit power for RF signals generated by the radiatingantenna are cycled within a range.
 9. The system of claim 1, wherein thetransmit power for signals generated by the radiating antenna isdetermined based on the number of documents present as determined by anumbering mechanism.
 10. The system of claim 1, further comprisingdetuning pads positioned on the top or bottom of the slot.